This invention relates to a stored-energy operating device, and more particularly to such a device which includes means for damping of flywheel oscillation.
The invention is more specifically concerned with improvements in the general type of stored-energy operating device disclosed in U.S. Pat. Nos. 2,829,737--Favre and 2,909,629--McCloud. The operating devices disclosed in these patents each comprise a heavy spring which is charged by the action of a small electric motor rotating a spring-controller, or flywheel, into a dead-center position, corresponding to the maximum compression of the spring. Rotation of the spring-controller is continued until it reaches a predetermined position, slightly past dead center, where it is held by suitable releasable stop means. When the stop means is released, the heavy spring, which had been charged, quickly discharges, and this discharging action is utilized to produce closing of the circuit breaker.
To prevent damage to several parts of the device when the spring-controller is driven against the above-described stop after charging of the spring, a releasable coupling must be provided between the motor and the spring-controller. In a preferred operating device, the releasable coupling takes the form of a pawl and abutment drive such as the one described in copending application of Barkan, Ser. No. 702,328, filed July 2, 1976, entitled "Stored-Energy Operating Device for an Electric Circuit Breaker". This application is assigned to the assignee of the present application and is hereby incorporated by reference in the present application. In this preferred operating device, after the spring has been fully charged and just prior to the instant that the stop is encountered by the spring-controller, the pawl is released from the cooperating abutment, thus uncoupling the motor from the spring-controller. At approximately the same time, the motor is deenergized and allowed to coast to a halt without interference to the stop.
In the type of stored-energy device described above, the spring, upon discharging to close the circuit breaker, drives the spring-controller in a forward direction into a second dead-center position with respect to the spring which is angularly spaced 180.degree. from the first dead-center position. Any excess energy remaining after this operation carries the spring-controller, or flywheel, in a forward direction past the second dead-center position, thus partially recharging the spring. Immediately after this partial recharging, the spring again discharges, driving the spring-controller in a reverse direction through the second dead-center to again partially recharge the spring. These oscillations of the spring-controller about the second dead-center continue at constant frequency, but with decreasing amplitude, until the excess energy is finally dissipated and the spring-controller comes to rest at the second dead-center position.
A problem presented by these oscillations is that it is necessary to immediately reenergize the charging motor in order to recharge the spring in the shortest possible time. It is therefore necessary that the oscillations be damped out by the time the motor-driven abutment reaches the pawl and begins transmitting recharging energy from the motor to the spring. Typically, a time of one to three seconds elapses between the release of the charged spring and the reengagement of the charging motor with the spring. Hence, it is necessary that the natural oscillations of the spring-controller be essentially damped out within one second. The inherent friction in the system is generally insufficient to damp these oscillations within such a short time. This is due to the fact that the inherent friction in the system is generally low in order to permit efficient use of the closing spring energy. My previously mentioned copending patent application suggested minimizing this problem by employing a continuously acting damper brake (see FIG. 4 of my copending application). However, although this is a solution to the oscillation problem, the use of such continuous damping adversely affects mechanism life, energy requirements and the torque magnitude imposed on the driving motor.
Accordingly, it is a general object of my invention to provide damping means which is operable only during a predetermined portion of rotation of the spring-controller.
Another object of my invention is to provide such damping means in the form of a simple part which can be easily incorporated into a stored-energy operating device such as the one shown in my previously mentioned copending patent application.
Another object of my invention is to provide such damping means which is operable substantially only during that portion of rotation of the spring-controller for which the previously mentioned oscillations occur.
Another object of my invention is to provide such damping means operable substantially after the useful work of the closing spring has been accomplished so that no significant penalty in the operating efficiency of a stored-energy operating device results.
Another object of my invention is to provide such damping means whose operation does not substantially increase the peak torque required for charging the closing spring.